Sulphide detection

Figure Bl.6.12 Ionization-energy spectrum of carbonyl sulphide obtained by dipole (e, 2e) spectroscopy [18], The incident-electron energy was 3.5 keV, the scattered incident electron was detected in the forward direction and the ejected (ionized) electron detected in coincidence at 54.7° (angular anisotropies cancel at this magic angle ). The energy of the two outgoing electrons was scaimed keeping the net energy loss fixed at 40 eV so that the spectrum is essentially identical to the 40 eV photoabsorption spectrum. Peaks are identified with ionization of valence electrons from the indicated molecular orbitals.

Hydrogen sulphide is a colourless gas, b.p. 213 K, with a most unpleasant odour the gas is very toxic, but the intense odour fortunately permits very minute concentrations of the gas to be detected. 

Upon fusion with caustic alkah (for experimental details, see Section IV,33,2) and acidification of the aqueous extract, hydrogen sulphide is evolved (detected by lead acetate paper). This test is given by aU organic compounds of divalent sulphur (RSH, R SR" and R SSR"). 

In order to detect these elements in organic compounds, it is necessary to convert them into ionlsable inorganie substanees so that the ionic tests of inoiganio qualitative analysis may be applied. This conversion may be accomplished by several methods, but the best procedure is to fuse the organic compound with metallio sodium (Lassalgne s test). In this way sodium cyanide, sodium sulphide and sodium halides are formed, which are readily identified. Thus ... 

Sulphur, as sulphide ion, is detected by precipitation as black lead sulphide with lead acetate solution and acetic acid or with sodium plumbite solution (an alkaLine solution of lead acetate). Halogens are detected as the characteristic silver halides by the addition of silver nitrate solution and dilute nitric acid the interfering influence of sulphide and cyanide ions in the latter tests are discussed under the individual elements. 

When an organic compound is heated with a mixture of zinc powder and sodium carbonate, the nitrogen and halogens are converted into sodium cyanide and sodium hahdes respectively, and the sulphur into zinc sulphide (insoluble in water). The sodium cyanide and sodium hahdes are extracted with water and detected as in Lassaigne s method, whilst the zinc sulphide in the residue is decomposed with dilute acid and the hydrogen sulphide is identified with sodium plumbite or lead acetate paper. The test for nitrogen is thus not affected by the presence of sulphur this constitutes an advantage of the method. 

Sulphur. Moisten the centre of a filter paper with sodium plumbite solution. Add about 10 ml. of dilute hydrochloric acid to the residue in the dish and immediately cover it with the prepared filter paper. If zinc sulphide is present in the residue, a dark brown stain, visible on the upper surface of the paper, will be obtained frequently the presence of hydrogen sulphide can also be detected by its odour. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

LPG is considered to be non-toxic witli no chronic effects, but the vapour is slightly anaesthetic. In sufficiently high concentrations, resulting in oxygen deficiency, it will result in physical asphyxiation. The gases are colourless and odourless but an odorant or stenching agent (e.g. methyl mercaptan or dimethyl sulphide) is normally added to facilitate detection by smell down to approximately 0.4% by volume in air, i.e. one-fifth of the lower flammable limit. The odorant is not added for specific applications, e.g. cosmetic aerosol propellant. 

Sulphur.—The presence of sulphur in organic compounds may be detected by heating the substance with a little metallic sodium or potassium. The alkaline sulphide, when dissolved in water, gives a violet colouration with a solution of sodium nitro-prusside. Heat a fragment of gelatine with a small piece of potassium in a test-tube until the bottom of the tube is red hot, and place it m a small beaker of water as described in the test for nitrogen (p. 2). Filter the liquid and add a few drops of sodium nitroprusside solution. 

Discussion. The theory of the titration of cyanides with silver nitrate solution has been given in Section 10.44. All silver salts except the sulphide are readily soluble in excess of a solution of an alkali cyanide, hence chloride, bromide, and iodide do not interfere. The only difficulty in obtaining a sharp end point lies in the fact that silver cyanide is often precipitated in a curdy form which does not readily re-dissolve, and, moreover, the end point is not easy to detect with accuracy. 

Olah and coworkers56 found that treatment of dialkyl, arylalkyl and diaryl sulphides with nitronium hexafluorophosphate (or tetrafluoroborate) 32 at —78° in methylene chloride resulted in the formation of sulphoxides in moderate to high yields (Table 3). In the oxidation of diphenyl sulphide which affords diphenyl sulphoxide in 95% yield, small amounts of the ring nitration products (o- and p-nitrophenyl phenyl sulphides) were formed. However, diphenyl sulphone and nitrophenyl phenyl sulphoxide were not detected among the reaction products. 

Do not rely on the sense of smell to detect hydrogen sulphide leaks. Strips of v/et lead acetate paper turn black on exposure to hydrogen sulphide and offer a simple indicator, as do colour indicator tubes. For plant-scale operations, instrumental multi-point detectors and alarms are likely to be more appropriate. 

The colour is the most obvious and conspicuous external property of a large number of minerals. Minerals are distinguished by an extraordinary variety of colours and shades of varying richness and intensity. Some mineral species are characterised by a constant colour, which enables one to detect them almost unerroneously. Just as an example, mention may be made of a sulphidic mineral of copper, bomite (Cu5FeS4). The best identifying feature of this mineral is its purplish-blue tarnish over a bronze colour ( peacock ore). 

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